Rear Bumper Guard Bolt Finish?

[BlackoutSteve]

Hey Guys.
1969 UPC 14-B2 Item 6, Screw asm 9419385. These are 5/16-18 that are not listed in the AMK caralog.
I would like to know the correct finish of these bolts please.
Phosphate/oil -S2? Silver zinc -S8? Silver Cadmium -S7? Black painted -S3? Chrome -S13? Stainless -S45?

I am also assuming a conical washer, hex head (like B-11910 pg 102)

Thanks. 

[JohnZ]

They're phosphate on my '69 Z/28.

[BlackoutSteve]

Thanks John.